Expression of a novel splice variant of FRMD7 in developing human fetal brains that is upregulated upon the differentiation of NT2 cells.

Yingzhi Li,Baorong Zhang,Jiali Pu

doi:10.3892/etm.2014.1916

Abstract

FRMD7 mutations are associated with X-linked idiopathic congenital nystagmus (ICN); however, the underlying mechanisms whereby mutations of FRMD7 lead to ICN remain unclear. In a previous study, the first FRMD7 splice variant (FRMD7-S) was cloned and identified, and FRMD7-S was hypothesized to play a significant role in neuronal differentiation and development. The present study investigated a novel multiple exon-skipping mRNA splice variant of FRMD7, termed FRMD7_SV2, which was detected in NT2 cells using northern blotting. The mRNA expression levels of FRMD7_SV2 in the developing human fetal brain were examined using reverse transcription polymerase chain reaction (PCR), while the expression levels in NT2 cells treated with retinoid acid (RA) or bone morphogenetic protein-2 were investigated using quantitative PCR. The results revealed that the expression of FRMD7_SV2 was spatially and temporally restricted in human fetal brain development, and was upregulated upon RA-induced neuronal differentiation of the NT2 cells. These results indicated that as a novel splice variant of FRMD7, FRMD7_SV2 may play a role in neuronal development.

Highlights

Idiopathic congenital nystagmus (ICN) is an oculomotor disorder characterized by involuntary oscillation of the eyes, with an onset at birth or within the first six months of life and an estimated global prevalence of 24 in 10,000 births [1]
(FRMD7_FL) cDNA, RT‐polymerase chain reaction (PCR) experiments were performed on the RNA extracted from the NT2 cells using a pair of specific primers
The splice variant was termed FRMD7_SV2 (Fig. 1C‐E). This multiple exon‐skipping event eliminated 227 nucleotides of the FRMD7_FL gene and resulted in a frameshift mutation that altered 19 amino acids prior to the premature termination at codon 39 (TGA), predicted to lead to the synthesis of a severely truncated protein based on the sequence (Fig. 1A)

Summary

Introduction

Idiopathic congenital nystagmus (ICN) is an oculomotor disorder characterized by involuntary oscillation of the eyes, with an onset at birth or within the first six months of life and an estimated global prevalence of 24 in 10,000 births [1]. ICN is genetically heterogeneous, and X‐linked ICN is the most common mode of inheritance. Three genetic loci responsible for X‐linked ICN have been mapped to chromosomes Xp11.3‐p11.4 [2], Xp22 [3,4] and Xq26‐Xq27. The FERM domain‐containing protein 7 (FRMD7) at Xq26‐Xq27 has been identified as responsible for X‐linked ICN [5,6]. Two novel missense mutations of the FRMD7 gene in the Chinese population have been reported [7], and to date, >40 mutations have been identified [8,9]. The biochemical role of FRMD7 in neural development and the mechanisms whereby mutations of FRMD7 lead to X‐linked ICN remain unclear

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Conclusion